Nolan's World War II drama was so shrouded in secrecy that hardly anyone on set was allowed to read the script.

Few productions in the history of the movies have been as shrouded in secrecy as Christopher Nolan’s “Dunkirk.” While filmmakers often go to great lengths to prevent their screenplays from leaking to the public, Nolan kept the script for “Dunkirk” so guarded that even very few members of the crew ever laid eyes on it.

Of the more than 600 people who helped bring Nolan’s World War II drama to life, the 20 or so crew members on set who were allowed to read the script included the director of photography, production designer, first assistant director and property master.

“It was a lot of guessing,” said “Dunkirk” art director Stéphane Cressend, who was only allowed to read the script once, six weeks after shooting began. “This is what’s really different from all the other productions I’ve worked on, because you always get the script first.” An art director on films like “The Hunger Games,” Martin Scorsese’s “Hugo” and the thriller “Now You See Me,” Cressend added that working without a script didn’t make “Dunkirk” more challenging than his other productions.

“It’s not harder, it’s just a different way to work,” he said. “You have to get accustomed to a new way of seeing the movie.”

Christopher Nolan and members of the crew of “Dunkirk” on location in the Netherlands.

Fokke Baarssen/REX/Shutterstock

How did Cressend know what kind of look Nolan wanted for the film? “You really have to trust the people you work with, like the supervising art director and the production designer,” he said. “When you get to read the script, you know you are really lucky, and you know that you are going to explain what you read to all of your crew, so you try not to forget anything.”

Nolan’s penchant for secrecy on “Dunkirk” extended beyond just the screenplay. Almost no one on set ever saw an image of what was being filmed, as the filmmaker had no monitors on set, aside from a small wireless device with an antenna that he kept for himself.

“It looked like a radio from the 1980s,” said key on-set dresser Octavio Tapia. “Normally when you’re working on a big film like this, you have a video village with big TV’s and you can see the scene.” Tapia read the screenplay a month before production, taking notes to help retain information related to the set decoration. “When you take notes, it’s almost like you’re rewriting the script,” he said.

Perhaps unsurprisingly, no photos were allowed on the “Dunkirk” set. Tapia and script supervisor Steve Gehrke were the only two people allowed to take photos, both for continuity purposes. One member of the costume department almost got fired for taking a photo of a soldier’s costume for continuity, according to Tapia. “It was a really big deal,” he said.

While members of the cast of “Dunkirk” did receive personal hard copies of the script, that didn’t prevent them from being roped into the production’s extreme levels of secrecy. At the New York premiere of “Dunkirk” on Tuesday, Kenneth Branagh, who played the role of Naval Commander Bolton, told Variety that he had to personally return a hard copy of the screenplay to Nolan after a round of script revisions. “I had to fly to Los Angeles and hand it directly back to him,” Branagh said. “I felt like I was on a spy film.”